Hydropneumatic devices for pressure transmission, used for example for riveting devices, are already known in a wide variety of embodiments.
Such devices have a working piston and a transmitter piston for transmitting pressure to the working piston, wherein, for the provision of a working force by the working piston, the transmitter piston, which is subjected to pneumatic action, dips into a hydraulic fluid and displaces hydraulic fluid in accordance with the positive displacement principle, and wherein the working piston, in a force stroke, is moved in a working direction by the displaced hydraulic fluid with a force transmission ratio corresponding to the effective piston surface areas.
Also provided is an accumulator piston which, before the force stroke, assists a rapid traverse movement of the working piston during a first stroke and, during a rapid-traverse stroke, assists the replenishment flow of hydraulic fluid.
Furthermore, between the transmitter piston and the accumulator piston, a pneumatic pressure may be realized which effects a pneumatic return movement of the transmitter piston when the operating pressure no longer acts on the transmitter piston. Furthermore, the accumulator piston is also permanently subjected to the action of a pneumatic initial pressure such that the hydraulic fluid volume present in the accumulator piston in an accumulator chamber is subjected to the corresponding pressure, or a preload.
For the return movement of the transmitter piston, a pneumatic pressure which is reduced in relation to the operating pressure is predefined on a return stroke side of the transmitter piston, such that the pneumatic return movement of the transmitter piston is effected by means of the pressure between the accumulator piston and the transmitter piston, this also being referred to as an air spring.
The air spring pressure acts permanently on the transmitter piston and accumulator piston and is always constant regardless of the state of movement of the pistons subjected thereto, and is, for example, approximately 0.6 bar.
In the case of a mechanical spring that may alternatively be provided, which spring acts under a preload between the transmitter piston and the accumulator piston, different pressures or forces always act as a result of the different operating states, in contrast to the situation with the air spring.